Sensor failure diagnosis in a pump monitoring system

ABSTRACT

A pump monitoring system for use in wellbore operations can determine whether an indication of a failure is due to an actual pump issue or a failed sensor. The pump monitoring system includes a sensor on a fluid end of a pump to measure properties associated with the pump and a vibration detector. A computing device executes instructions to receive the sensor signal and the vibration signal and identify an irregularity in the sensor signal. The processor then determines whether an operational signal component is present in the vibration signal, and displays an indication that the sensor has failed when the operational signal component is not present in the vibration signal. If the operational signal component is present in the vibration signal, the irregularity is likely caused by a pump problem such as a failed valve.

TECHNICAL FIELD

The present disclosure relates generally to pressure pumps and, moreparticularly (although not necessarily exclusively), to using signalprocessing to identify a failed sensor.

BACKGROUND

Pressure pumps may be used in wellbore treatments. For example,hydraulic fracturing may utilize a pressure pump to introduce or injectfluid at high pressures into a wellbore to create cracks or fractures indownhole rock formations. A processor-based pump monitoring system canbe used to detect problems such as possible failures or poor pumpperformance by measuring such properties as strain, position, torque,and flow. When an indicator or signal graph indicates a problem,maintenance personnel can investigate the cause and take correctiveaction. The time taken to investigate the problem results in downtimefrom the pumping operations. Sometimes, parts are unnecessarily replacedwhen the time needed to specifically isolate the problem is significant,adding to the cost of maintenance operations. For example, sometimesparts of a pump section are replaced when the problem indicator is dueto a failed sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional, top view schematic diagram depicting anexample of a pressure pump that may be connected to a pump monitoringsystem according to one aspect of the present disclosure.

FIG. 1B is a cross-sectional, side view schematic diagram depicting thepressure pump of FIG. 1A according to one aspect of the presentdisclosure.

FIG. 2 is a block diagram depicting a pump monitoring system for apressure pump according to aspects of the present disclosure.

FIG. 3 is a screen shot of an example pump monitoring system interfaceaccording to some aspects.

FIG. 4 is a signal graph depicting a waveform representing the internalcylinder pressure of a pump section according to some aspects.

FIG. 5 is a signal graph depicting example waveforms for suctionpressure and discharge pressure superimposed over the internal cylinderpressure waveform of FIG. 4 according to some aspects.

FIG. 6 is a signal graph depicting the output of an envelope filter asapplied the cylinder pressure signal waveform of FIG. 4 according tosome aspects.

FIG. 7 is a signal graph showing strain signals from strain gaugesrepresenting strain in several cylinders of a pump according to someaspects.

FIG. 8 is a signal graph depicting the resultant strain signals afterthe strain signals in FIG. 7 have been aligned and zeroed.

FIG. 9 is a signal graph showing a scaled strain signal that exhibitsvalve actuation points according to some aspects of the disclosure.

FIG. 10 is a signal graph showing discharge strain signals for severalcylinders of a pump according to some aspects.

FIG. 11 is a signal graph showing a combined discharge strain signalaccording to some aspects of the disclosure.

FIG. 12 is a signal graph showing discharge pressure associated with adischarge valve in a pump section as obtained by correlating a strainsignal to discharge pressure according to some embodiments of thedisclosure.

FIG. 13 is an example of a finite element model used to determine normalstrain values for a pump being monitored by the pump monitoring systemaccording to some aspects.

FIG. 14 is a flowchart illustrating the process executed by a pumpmonitoring system to specifically identify a failed valve in a sectionof a pump according to some aspects of this disclosure.

FIG. 15 is signal graph of an output of a vibration sensor attached to apump section as obtained by a pump monitoring system according to someaspects.

FIG. 16 is a flowchart illustrating the process executed by a pumpmonitoring system to specifically identify a failed sensor in a sectionof a pump according to some aspects of this disclosure.

FIG. 17 is a detailed view of a portion of an interface like that shownin FIG. 3 , but indicating a specific valve failure according toexamples of aspects of the disclosure.

FIG. 18 is a detailed view of a portion of an interface like that shownin FIG. 3 , but indicating a strain sensor failure according to examplesof aspects of the disclosure.

DETAILED DESCRIPTION

Certain aspects of the present disclosure relate to a pump monitoringsystem that can determine whether an indication of a failure is due toan actual pump issue or other phenomena, such as failed or failingsensor. While the sensors used for pump monitoring, if installedproperly, are very robust, the installation process can be problematicfor field or camp installation and repair. A typical sensor failureincludes a de-bonding of the sensor form the target, which is typicallya portion of the fluid end of a pump. This de-bonding can be total orpartial, and can cause the system to incorrectly indicate variousdegrees of valve failure. By adding one or more additional measurementsto the pump monitoring system, a sensor that has failed either bybecoming de-bonded or for any other reason can be positively identifiedso that specific corrective action can be taken.

The enhanced ability for a pump monitoring system to self-diagnoseresults in part from the addition of a robust vibration detector. Thecorresponding pump failure that is typically indicated when a sensorcomes loose is a totally blown valve. A totally blown valve will createa unique vibration signature that is timed to the pump. If thisvibration signature is present along with the failure indication, anoperator can assume with substantial certainty that the pump monitoringsystem is functioning properly and that the failure indication isaccurate. If the vibration signature is not present, then a warningmessage to perform maintenance on a specific sensor can be delivered tothe operator in the form of an indication that a sensor has failed.

Automated detection of bad sensors helps reduce maintenance time andcosts for a pump monitoring system. It may also be possible to eliminatescheduled sensor checks and valve checks as part of the maintenance of apump. Pump maintenance can be based on insert life, appearance, and thewear of the steel valve body and seat. The wear on these components issteady and gradual and can be observed to estimate remaining life onthese components. Making use of the diagnostic technique describedherein can increase the possibility of completing a well withoutregularly scheduled maintenance, only changing valves or checkingsensors when needed or between jobs.

In some examples, a pump monitoring system for use in wellboreoperations includes a sensor on a fluid end of a pump to measureproperties associated with the pump and provide a sensor signal, as wellas a vibration detector to measure vibration associated with the pumpand provide a vibration signal. A computing device can be connected tothe sensor and the vibration detector, and includes a processor that canexecute instructions to receive the sensor signal and the vibrationsignal and identify an irregularity in the sensor signal. The processorthen determines whether an operational signal component is present inthe vibration signal, and displays an indication that the sensor hasfailed when the operational signal component is absent from thevibration signal. If the operational signal component is present in thevibration signal, the irregularity is likely caused by a pump problemsuch as a failed valve.

In some examples, determining whether the operational signal componentis present in the vibration signal further includes detecting a squarewave like component in the vibration signal. In some examples, thesquare wave like component is detected by applying an order trackingfilter to the vibration signal. In examples, the square wave likecomponent is detected by correlating the vibration signal to a strainsignal. The vibration detector can include, as examples, anaccelerometer, an acoustic transducer, a vibration transducer, or atorque transducer positionable at a torque input for a pump section thatincludes the sensor.

These illustrative examples are given to introduce the reader to thegeneral subject matter discussed here and are not intended to limit thescope of the disclosed concepts. The following sections describe variousadditional features and examples with reference to the drawings in whichlike numerals indicate like elements, and directional descriptions areused to describe the illustrative aspects but, like the illustrativeaspects, should not be used to limit the present disclosure.

These illustrative examples are given to introduce the reader to thegeneral subject matter discussed here and are not intended to limit thescope of the disclosed concepts. The following sections describe variousadditional features and examples with reference to the drawings in whichlike numerals indicate like elements, and directional descriptions areused to describe the illustrative aspects but, like the illustrativeaspects, should not be used to limit the present disclosure.

FIG. 1A and FIG. 1B show views of an example pressure pump 100 that isbeing monitored by a pump monitoring system according to certain aspectsof the present disclosure. The pressure pump 100 is a positivedisplacement pressure pump. The pressure pump 100 includes a power end102 and a fluid end 104. The power end 102 is coupled to a motor,engine, or other prime mover for operation. The fluid end 104 includeschambers 106 for receiving and discharging fluid flowing through thepressure pump 100. Although FIG. 1A shows three chambers 106 in thepressure pump 100, a pressure pump may include any number of chambers106, including one, without departing from the scope of the presentdisclosure. In the examples presented herein, chambers 106 are sometimesalso referred to as “cylinders.”

The pressure pump 100 includes a rotating assembly. The rotatingassembly includes a crankshaft 108, one or more connecting rods 110, acrosshead 112, plungers 114, and related elements (e.g., pony rods,clamps, etc.). The crankshaft 108 is positioned on the power end 102 ofthe pressure pump 100 and is mechanically connected to a plunger in achamber 106 of the pressure pump via the connecting rod 110 and thecrosshead 112. The crankshaft 108 may include an external casing orcrankcase. The crankshaft 108 causes a plunger 114 located in a chamber106 to displace any fluid in the chamber 106. In some aspects, eachchamber 106 of the pressure pump 100 includes a separate plunger 114,and each plunger 114 in each chamber 106 is mechanically connected tothe crankshaft 108 via the connecting rod 110 and the crosshead 112.Each chamber 106 includes a suction valve 116 and a discharge valve 118for absorbing fluid into the chamber 106 and discharging fluid from thechamber 106, respectively. A chamber 106, suction valve 116, dischargevalve 118 and their associated manifold portions may be referred to as apump section. The fluid is absorbed into and discharged from the chamber106 in response to a movement of the plunger 114 in the chamber 106.

A suction valve 116 and a discharge valve 118 are included in eachchamber 106 of the pressure pump 100. In some aspects, the suction valve116 and the discharge valve 118 are passive valves though the processdescribed herein would work for driven valves as well. As the plunger114 operates in the chamber 106, the plunger 114 imparts motion andpressure to the fluid by direct displacement. The suction valve 116 andthe discharge valve 118 open and close based on the displacement of thefluid in the chamber 106 by the operation of the plunger 114. Thesuction valve 116 is opened during a recession of the plunger 114 toprovide absorption of fluid from outside of the chamber 106 into thechamber 106. As the plunger 114 is withdrawn from the chamber 106, apartial suction is created to open the suction valve 116 to allow fluidto enter the chamber 106. The fluid is absorbed into the chamber 106from an inlet manifold 120. Fluid already in the chamber 106 moves tofill the space where the plunger 114 was previously located in thechamber 106. The discharge valve 118 is closed during this process.These operations cause mechanical vibrations. Block 121 is a mountingposition for an accelerometer to provide a vibration signal as part of apump monitoring system, as described later.

The discharge valve 118 is opened as the plunger 114 moves forward orreenters the chamber 106. As the plunger 114 moves further into thechamber 106, the fluid is pressurized. The suction valve 116 is closedduring this time to allow the pressure on the fluid to force thedischarge valve 118 to open and discharge fluid from the chamber 106.The discharge valve 118 discharges the fluid into a discharge manifold122. The loss of pressure inside the chamber 106 allows the dischargevalve 118 to close. Together, the suction valve 116 and the dischargevalve 118 operate to provide the fluid flow in a desired direction. Theprocess may include a measurable amount of pressure and stress in thechamber 106, the stress resulting in strain to the chamber 106 or fluidend 104 of the pressure pump 100. The pump monitoring system, if coupledto the pressure pump 100 gauges the strain. Block 123 shows an exampleplacement point for a discharge pressure transducer, mounted in thedischarge manifold 122. This pressure transducer measures pressure inthe discharge manifold. A similar pressure transducer (not visible) ismounted in the inlet manifold and measures the pressure in the suctionmanifold. It can be said that on the discharge side the valves must holdthe discharge pressure back, and on the suction side, the suctionpressure is what is supplying the suction valve.

In certain aspects, a pump monitoring system is coupled to the pressurepump 100 to gauge the strain and determine actuation of the suctionvalve 116 and the discharge valve 118. The pump monitoring system, asdescribed herein, can also specifically identify failed valves andfailed sensors. An example pump monitoring system as described hereinincludes strain gauges positioned on an external surface of the fluidend 104 to gauge strain in the chambers 106. Blocks 124 in FIG. 1A showexample placements for each of the strain gauges. In some aspects, amonitoring system includes one or more position sensors for sensing theposition of the crankshaft 108. Measurements of the crankshaft positionmay allow the monitoring system to determine the position of theplungers 114 in the respective chambers 106. A position sensor of themonitoring system may be positioned on an external surface of thepressure pump 100. Block 126 shows an example placement of a positionsensor on an external surface of the power end 102 to sense the positionof the crankshaft 108. In some aspects, measurements from the positionsensor may be correlated with the measurements from the strain gauges todetermine actuation delays corresponding to the valves 116, 118 in eachchamber 106 of the pressure pump 100 for identifying cavitation in thefluid end 104.

FIG. 2 is a block diagram showing an example of a pump monitoring system200 coupled to the pressure pump 100. The pump monitoring system 200includes multiple sensors and a computing device 206. The pumpmonitoring system may include a torque sensor 201. A position sensor 202and a strain gauge or strain gauges 203 are coupled to the pressure pump100. The position sensor 202 may include a single sensor or mayrepresent an array of sensors. The position sensor 202 may be a magneticpickup sensor capable of detecting ferrous metals in close proximity.The position sensor 202 may be positioned on the power end 102 of thepressure pump 100 for determining the position of the crankshaft 108. Insome aspects, the position sensor 202 may be placed proximate to a pathof the crosshead 112. In other aspects, the position sensor 202 may beplaced on the power end 102 as illustrated by block 126 in FIG. 1A.

The strain gauge 203 is positioned on the fluid end 104 of the pressurepump 100. The strain gauge 203 may include a single gauge or an array ofgauges for determining strain in the chamber 106. Non-limiting examplesof types of strain gauges may include electrical resistance straingauges, semiconductor strain gauges, fiber optic strain gauges,micro-scale strain gauges, capacitive strain gauges, vibrating wirestrain gauges, etc. In some aspects, the pump monitoring system 200 mayinclude a strain gauge 203 for each chamber 106 of the pressure pump 100to determine strain in each of the chambers 106, respectively. In someaspects, the strain gauge 203 is positioned on an external surface ofthe fluid end 104 of the pressure pump 100 in a position subject tostrain in response to stress in the chamber 106. For example, the straingauge 203 may be positioned on a section of the fluid end 104 in amanner such that when the chamber 106 loads up, strain may be present atthe location of the strain gauge 203. The strain gauge 203 may be placedon an external surface of the pressure pump 100 in a location directlyover the plunger bore corresponding to the chamber 106 as illustrated byblocks 124 in FIG. 1A to measure strain in the chamber 106. The straingauge 203 generates a signal representing strain in the chamber 106 andtransmits the signal to a processor 208. The pump monitoring system 200of FIG. 2 includes accelerometer 207, the placement of which isdiscussed above with respect to FIG. 1B. The pump monitoring system 200of FIG. 2 also includes the suction pressure transducer 204, discussedabove, and the discharge pressure transducer 205, the placement of whichis discussed above with respect FIG. 1B. The accelerometer and pressuretransducers generate vibration and pressure signals and transmit thesesignals to processor 208.

The computing device 206 is coupled to the position sensor 202, thestrain gauge 203, and the other sensors and transducers. The computingdevice 206 includes the processor 208, a bus 210, and a memory 212. Insome aspects, the pump monitoring system 200 may also include a displayunit 214. The processor 208 may execute instructions 216 including oneor more operations for identifying failed valves or a failed sensor. Theinstructions 216 may be stored in the memory 212 coupled to theprocessor 208 by the bus 210 to allow the processor 208 to perform theoperations. The processor 208 may include one processor or multipleprocessors. Non-limiting examples of the processor 208 may include aField-Programmable Gate Array (“FPGA”), an application-specificintegrated circuit (“ASIC”), a microprocessor, etc.

The non-volatile memory 212 may include any type of memory device thatretains stored information when powered off. Non-limiting examples ofthe memory 212 may include electrically erasable and programmableread-only memory (“EEPROM”), a flash memory, or any other type ofnon-volatile memory. In some examples, at least some of the memory 212may include a medium from which the processor 208 can read theinstructions 216. A non-transitory, computer-readable medium may includeelectronic, optical, magnetic or other storage devices capable ofproviding the processor 208 with computer-readable instructions or otherprogram code (e.g., instructions 216). Non-limiting examples of acomputer-readable medium include (but are not limited to) magneticdisks(s), memory chip(s), ROM, random-access memory (“RAM”), an ASIC, aconfigured processor, optical storage, or any other medium from which acomputer processor can read the instructions 216. The instructions 216may include processor-specific instructions generated by a compiler oran interpreter from code written in any suitable computer-programminglanguage, including, for example, C, C++, C#, etc. In some examples, thecomputing device 206 determines an input for the instructions 216 basedon sensor data 218 and strain data 219 input into the computing device206. Stored strain data 219 can be acquired by test operation of thepump or finite element analysis.

In some aspects, the computing device 206 may generate interfacesassociated with the sensor data 218 and information generated by theprocessor 208 therefrom to be displayed via a display unit 214. Thedisplay unit 214 may be coupled to the processor 208 and may include anyCRT, LCD, OLED, or other device for displaying interfaces generated bythe processor 208. In some aspects, the display unit 214 may alsoinclude audio components. The computing device 206 may generate audibleinterfaces associated with information generated by the processor 208(e.g., alarms, alerts, etc.).

In some aspects, in addition to the pump monitoring system 200, thepressure pump 100 may also be coupled to a wellbore 220. For example,the pressure pump 100 may be used in hydraulic fracturing to injectfluid into the wellbore 220. Subsequent to the fluid passing through thechambers 106 of the pressure pump 100, the fluid may be injected intothe wellbore 220 at a high pressure to break apart or otherwise fracturerocks and other formations adjacent to the wellbore 220 to release orotherwise stimulate hydrocarbons. The pump monitoring system 200 maymonitor the flow of the fluid through the pressure pump 100 to determinethe rate of injection of the fluid into the wellbore 220. Althoughhydraulic fracturing is described here, the pressure pump 100 may beused for any process or environment requiring a positive displacementpressure pump.

FIG. 3 is a screen shot of an example pump monitoring system interface300. This interface 300 is for pump monitoring system 200. In thisexample, the pump monitoring system 200 is connected to a pump with fivepump sections (“pots”) instead of three pump sections as previouslyillustrated. In this example, the interface 300 is output to displayunit 214 of FIG. 2 by processor 208 of FIG. 2 to provide sensorinformation to a user. Interface 300 includes seven panels. Panel 302 isa position display provided by position sensor 202 of FIG. 2 . Thispanel shows relative position on the vertical axis and time on thehorizontal axis. The position provided is that of a single plunger;however, since all plungers are connected to the same crankshaft, panel302 provides an overall timing indication of the pump. Panel 304, panel306, panel 308, panel 310, and panel 312 each show a signal graph of astrain signal from a strain gauge 203 of FIG. 2 . The signals are forpot 1, pot 2, pot 3, pot 4, and pot 5, respectively. The strain signalgraphs show the strain signal in volts on the vertical axis as relatedto time on the horizontal axis. The time axes of all signal graphs arealigned. However, the signal graphs are all automatically scaled to showdetail and the vertical axes of all signal graphs are automaticallyadjusted accordingly.

Still referring to FIG. 3 , strain signal graphs 304, 306, 310, and 312,all display normal, expected strain for a pump section. The strainchanges with the stroke of the pump as indicated by panel 302. However,the strain signal graph shown in panel 308, for pot 3, shows an abnormalstrain signal. This abnormal strain signal identifies some failure inpot 3 of the pump. Interface panel 314 is a series of five pairs ofstatus indicators. The displayed pairs of indicators, from left toright, show the status of pot 1, pot 2, pot 3, pot 4, and pot 5. The topindicator of each pair is a status indicator for the discharge portionof the pump section, indicating the status of the discharge valve, andthe bottom indicator of each pair is a status indicator for the suctionportion of the pump section, indicating the status of the suction valve.In FIG. 3 , both status indicators for pot 3 are showing a failureindication, which in a physical display unit may be indicated by color,for example, red. Thus, status display panel 314 of FIG. 3 is indicatinga failure in pump section 3, but cannot provide more detail on the typeof failure. However, there are some circumstances where additionaldetail is provided by the status display panel of pump monitoring systeminterface 300, as described in more detail below.

FIG. 4 is a signal graph 400 depicting a waveform representing theinternal cylinder pressure of a pump section according to some aspects.This pressure was derived from a strain gauge 203 mounted externally.Pressure in units of psi is plotted on the vertical axis and time inunits of seconds is plotted on the horizontal axis. Pressure waveform402 shows a signal that includes a square wave like component. The upperportion 404 of the square wave of pressure waveform 402 is correlatedwith the discharge pressure of the pump section, and the lower portion406 is correlated with the suction pressure of the pump section.

FIG. 5 is a signal graph 500 depicting example waveforms for relativesuction pressure and discharge pressure as measured by a suctionpressure transducer 204 and a discharge pressure transducer 205,respectively. These pressure transducers provide relative pressure overtime for each valve in the pump section. These waveforms aresuperimposed over the internal cylinder pressure waveform 402 of FIG. 4. FIG. 5 shows the relative agreement between the pressure measured inthe cylinder as indicated by waveform 402 to both the relative dischargepressure indicated by waveform 504 the relative suction pressureindicated by waveform 506. The scale of the horizontal and vertical axesof signal graph 500 is the same as that of signal graph 400 of FIG. 4 .While the discharge pressure waveform 504 corresponds closely to thedischarge pressure portions of the cylinder pressure waveform 402, thereare some discrepancies with the correlation of the suction pressurewaveform 506 to the chamber pressure waveform. These discrepanciesresult from measuring the cylinder pressure with an external straingauge. The external strain gauge also measures the bending of the fluidend of the pump due to the other cylinders. This difference can beavoided by using an actual pressure transducer placed inside thecylinder, negated using averaging and filtering, or corrected usingmechanical theory and strain analysis.

Since, as shown above, the upper portion of the cylinder pressure datatrace represents the discharge pressure, an upper envelope of thecylinder pressure signal is a representation of the discharge pressure.Likewise, the lower envelop of the cylinder pressure signal wouldrepresent the suction pressure. Thus, the suction and dischargepressures can be derived using an envelope filter, as shown in FIG. 6 .FIG. 6 is a signal graph 600 depicting an output of an envelope filteras applied the cylinder pressure signal waveform of FIG. 4 . Signalgraph 600 shows envelope filter waveform 604 superimposed on cylinderpressure waveform 402, with the same time and pressure scales as shownin FIG. 4 . While only the upper envelop (discharge pressure) is shown,the same process can be used to produce a lower envelop (suctionpressure). The envelope filters used may be either digital or analog.The enveloping filters should have a rapid response and a slow decay toproperly simulate any missing part of the signal.

If higher sample rates are needed for better resolution of the actualpressure, readings from multiple cylinders can be combined. Such anapproach requires more sensors, and hence, more expense, as one sensorper pump section would be needed, however, in some pump monitoringsystems the sensors may already be present for other purposes. For theanalysis presented with respect to FIGS. 7-14 , it can be assumed thatmultiple strain signals are combined. In some aspects, the strainsignals from all cylinders in the pump are used.

FIG. 7 is a signal graph 700 showing strain signals from strain gaugesrepresenting strain in several cylinders of a pump according to someaspects. These signals represent strain while the pump is in operation.This strain data needs to be offset due to using non-zeroed straingauges for these measurements. As an example, strain signal 702 hasmaximum values that are higher than the other strain signals. Similarly,strain signal 704 has minimum values that are lower than the otherstrain signals. FIG. 8 is a signal graph 800 in which the strain signalsfrom FIG. 7 have been aligned and zeroed.

FIG. 9 shows how the strain data can be separated using the valveactuation points for both the suction and discharge valves. Morespecifically, the strain signal is separated into a suction strainsignal and a discharge strain signal. FIG. 9 shows the location of theseactuation points on an example waveform. Once the points are known thedischarge strain is the portion of the signal in between the dischargeopening and discharge closing points. Similarly, the suction portion isbracketed by the suction opening and suction closing points. FIG. 9shows signal graph 900 with a raw strain signal 901 generated by astrain gauge coupled to the fluid end of a pressure pump and positionedon an external surface. For purposes of this discussion it can beassumed this pressure pump is being monitored by pump monitoring system200. The strain signal 901 represents strain measured by the straingauge 203. The computing device 206 can determine the actuation points902, 904, 906, and 908 of the suction valve and the discharge valve forthe pump section based on the strain signal 901. The actuation points902, 904, 906, and 908 represent the points in time where the suctionvalve and the discharge valve open and close. For example, the computingdevice 206 may execute the instructions 216 stored in the memory 212 andincluding signal-processing algorithms to determine the actuation points902, 904, 906, and 908. For example, the computing device 206 mayexecute instructions 216 to determine the actuation points 902, 904,906, and 908 by determining discontinuities in the strain signal 901.The stress in the chamber changes during the operation of the suctionvalve and the discharge valve to cause the discontinuities in the strainsignal 901 during actuation of the valves and the computing device 206can identify the discontinuities as the opening and closing of thevalves. In one example, the strain in the chamber is isolated to thefluid in the chamber when the suction valve is closed. The isolation ofthe strain causes the strain in the chamber to load up until thedischarge valve is opened. When the discharge valve is opened, thestrain levels off until the discharge valve is closed, at which pointthe strain unloads until the suction valve is reopened. Thediscontinuities may be present when the strain signal 901 shows a suddenincrease or decrease in value corresponding to the actuation of thevalves.

In FIG. 9 , actuation point 902 represents the discharge valve opening,actuation point 904 represents the discharge valve closing, actuationpoint 906 represents the suction valve opening, and actuation point 908represents the suction valve closing again to resume the cycle of fluidinto and out of the chamber. In some aspects, the computing device 206may cause the display unit 214 to display the strain signal 901 and theactuation points 902, 904, 906, and 908 as shown in FIG. 9 . The exactmagnitudes of strain in the chamber determined by the strain gauge 203may not be required for determining the actuation points 902, 904, 906,and 908. The computing device 206 may determine the actuation points902, 904, 906, and 908 based on the strain signal 901 providing acharacterization of the loading and unloading of the strain for thechamber.

FIG. 10 is a signal graph 1000 showing discharge strain signals 1002 forseveral cylinders of a pump. These may then be combined to produce acontinuous discharge strain signal. FIG. 11 is a signal graph 1100showing a combined discharge strain signal 1102. Strain signal 1102 canbe correlated to pressure in various ways, such as testing, the use of afinite element analysis (FEA) model, or by correlating it to the actualsuction and discharge pressures as described herein.

The method described above can be used by computing device 206 to derivethe continuous discharge pressure signal of FIG. 12 . FIG. 12 is asignal graph 1200 showing a pressure signal 1202, which represents adischarge pressure associated with a discharge valve in a pump sectionas obtained by correlating a strain signal to discharge pressure. Thesame process is also used to derive the suction pressure. Suctionpressure results will typically be of lower resolution than thedischarge pressure results due to the reduced magnitudes experiencedduring the suction portion of the pump stroke. While the above methoddemonstrates the concept of how the measured cylinder strains from thepump monitoring system can be correlated to theoretical pressure, thestrains can also be directly correlated to the measured pressures,eliminating FEA modeling or other theoretical correlations, since twomeasured points are available to adjust the offset and slope of thestrain signals. The correlation between pressure and strain is used totranslate the signal of FIG. 11 into the signal of FIG. 12 .

When a valve fails in a pump like that shown in FIG. 1A and FIG. 1B, thestrain or pump pressure signal will become the level of either thedischarge pressure or the suction pressure. The processor needs to keepstored strain values for each strain sensor in order to use the currentstrain value to derive current pressure using the strain signal. Thesevalues can be acquired during a test operation of the pump when allvalves are known to be in good working order. Alternatively, thesevalues can be derived from FEA modeling data. FIG. 13 is an example of afinite element model 1300 that can be used for the correlation discussedpreviously, or to ascertain strain values, which can then be stored inmemory 212. In FIG. 13 , block 123, the placement point for thedischarge pressure transducer is also shown.

FIG. 14 is a flowchart illustrating the process 1400 executed by thepump monitoring system 200 of FIG. 2 to specifically identify a failedvalve in a section of a pump according to embodiments of thisdisclosure. Process 1400 makes use of at least some of the processingtechniques illustrated in FIGS. 4-12 . At block 1402, the monitoringsystem acquires and stores strain value data for the pump. This strainvalue data is stored in memory 212 as strain data 219. At block 1404,the system identifies a failed pump section by detecting irregularitiesin the strain signal received from a strain gauge 203. At block 1406,the computing device 206 of the pump monitoring system acquires thecylinder pressure from the strain signal. The computing device 206 alsoacquires the relative suction pressure, and the relative dischargepressure. The relative suction and discharge pressures are acquired frompressure transducers 204 and 205. At block 1408 computing system 206applies an envelope filter to the cylinder pressure signal asillustrated in FIG. 5 and FIG. 6 to obtain a discharge pressure portionand a suction pressure portion of the cylinder pressure signal. At block1410 of FIG. 14 , the computing device 206 separates the strain signalfrom the section into a suction strain signal and a discharge strainsignal. This separation can be accomplished by detecting actuationpoints as shown in FIG. 9 . To increase resolution, signals frommultiple cylinders can be combined as illustrated in FIG. 10 and FIG. 11. At block 1412, the computing device 206 correlates the strain signalto actual pressures associated with the specific valves, such as thecorresponding manifold pressures, in the pump section using the pressuresignals. In the case of the discharge valve, the strain signal iscorrelated to an actual discharge pressure in the pump section using adischarge pressure signal. In the case of the suction valve, the strainsignal is correlated to an actual suction pressure in the pump sectionusing the suction pressure signal.

Still referring to FIG. 14 , at block 1414, the pump monitoring systemcompares the current pump pressure to the actual discharge pressure andactual suction pressure as determined above. If the pump pressurecorresponds to an actual pressure of one of the valves in the pumpsection in question, a specific valve failure is indicated. If the pumppressure is equal to or very close to the suction pressure, a badsuction valve is indicated at block 1416. If the pump pressure is equalto or very close to the discharge pressure, a bad discharge valve isindicated at block 1418. These indications can be displayed on displayunit 214, and a specific display technique will be discussed below withrespect to FIG. 17 . In a multi-section pump like the example pump ofFIGS. 1A and 1B, the pump pressure may be the section pressure for thesection in question. For a single section pump, the terms “pumppressure” and “section pressure” are synonymous.

FIG. 15 is signal graph 1500 of an output signal 1502 of a vibrationdetector, in this example accelerometer 207, attached to a pump section.Signal 1502 has square wave components as suggested by the regular upperand lower magnitude spikes. Thus, signal 1502 has an operational signalcomponent, as one can appreciate by taking note of square-wave-likesignal graphs previously discussed. Point 1504 indicates a possibleleaky valve, though the possible leaky valve would likely be firstdetected by the valve failure determination method previously discussed.Referring to the pump monitoring system interface of FIG. 3, panel 308for pot 3 indicates an irregularity in the strain gauge signal aspreviously discussed. Since the accelerometer attached to pot 3 producesa signal with operational signal components, it is very likely that thestrain gauge, the sensor in this case, is reading properly. If theoperational signal were missing, it would be an indication that thestain gauge is defective or has come loose from its mounting. Theaddition of the accelerometer and appropriate computer program code toprocess the vibration signal in the pump monitoring system provides twoindependent methods for detecting a valve failure. If these two methodsdisagree, a sensor failure is strongly suspected and can beprogrammatically indicated.

FIG. 16 is a flowchart illustrating the process 1600 executed by a pumpmonitoring system to specifically identify a failed sensor in a sectionof a pump according to embodiments of this disclosure. At block 1602,the computing device 206 receives both a sensor signal and a vibrationsignal. The vibration signal comes from accelerometer 207. At block1604, the computer device 206 identifies an irregular sensor signal,such as an irregular signal from a strain gauge as previously discussed.At block 1606, a determination is made as to whether an operationalsignal component is present in the vibration signal from theaccelerometer. If not, at block 1608, a sensor failure indication isdisplayed on display unit 214 at block 1610. Otherwise, processingcontinues with signals continuing to be received and analyzed.

Although an accelerometer is given as an example, a vibration detectorcan be any sensor, gauge, or transducer from which a vibration signalcan be derived. Such a sensor includes not only an accelerometer, butalso an acoustic transducer, vibration transducer, or a torquetransducer. The torque transducer can be used to estimate angle of twistof certain drivetrain structural (torsion) components, the variation ofspeed of rotational drivetrain components, or directly measure thetorque in the drivetrain. For a torque transducer to be used as avibration detector, it should be placed at the torque input for a pumpsection. The operational signal component that is used to determine thevalidity of failure indications can be a similar to a square wave, butwith advanced signal processing techniques readily available other typesof signal components could be used. If a square wave is to be detected,it can be detected by applying an order tracking filter to identify thesquare wave component. A square wave component could also be detected bycomparing the vibration signal to a signal from a strain gauge, as boththe noise signature and square wave signature would typically be similarfrom these two sensors.

Any of the above techniques can be used to separately confirm a valvefailure and indicate a sensor failure if the valve failure cannot beconfirmed. However, the methodology may need to be changed to match thesensing technique for specific types or models of pumps or for empiricalmodels based on measurements, data and baselines. In each case themeasurement would confirm the failure read by the pump monitoring systemor it could indicate a problem with the integrity of the readings andalert an operator that maintenance of a sensor is required.

FIG. 17 is a detailed view of a portion of an interface like panel 314of FIG. 3 , but indicating a specific valve failure according to thevalve failure determination techniques described herein. FIG. 17includes pairs of virtual indicator “lights” 1702 in two rows, the toprow representing a discharge valve status and the bottom rowrepresenting a suction valve status. Each pair represents the status ofthe valves in a pot. Indicator light 1704 is displayed as darkened,though in an actual system a distinctive color might instead be used.Indicator light 1704 indicates a problem with the suction valve for pot3.

FIG. 18 is a detailed view of a portion of an interface like panel 314of FIG. 3 , but with additional “lights” for indicating a sensor failureas discussed above. FIG. 18 includes triplets of virtual indicator“lights” 1802 in three rows, the top row representing strain sensorstatus, the middle row representing discharge valve status, and thebottom row representing a suction valve status. Each triplet representsthe status for a specific pot. Indicator light 1806 is displayed asdarkened, though in an actual system a distinctive color might be used.It would also be possible to have a display like that shown in FIG. 17and just turn both indicators a specific color to indicate a sensorissue. In this example, indicator light 1806 indicates a problem withthe strain gauge for pot 3.

In some aspects, pump monitoring systems are provided according to oneor more of the following examples:

As used below, any reference to a series of examples is to be understoodas a reference to each of those examples disjunctively (e.g., “Examples1-4” is to be understood as “Examples 1, 2, 3, or 4”).

Example #1: A pump monitoring system for use in wellbore operationsincludes a sensor on a fluid end of a pump to measure propertiesassociated with the pump and provide a sensor signal and a vibrationdetector positionable to measure vibration associated with the pump andprovide a vibration signal. A computing device is couplable to thesensor and the vibration detector and includes a processor for whichinstructions executable by the processor are used to cause the processorto receive the sensor signal and the vibration signal, identify anirregularity in the sensor signal, determine, by processing thevibration signal, whether an operational signal component is present inthe vibration signal, and display an indication that the sensor hasfailed when the operational signal component is absent from thevibration signal.

Example #2: The pump monitoring system of example 1, wherein theinstructions are executable to detect a square wave like component inthe vibration signal.

Example #3: The pump monitoring system of example(s) 1 or 2, wherein theinstructions are executable to apply an order tracking filter to thevibration signal to detect the square wave like component.

Example #4: The pump monitoring system of example(s) 1-3 wherein theinstructions are executable to correlate the vibration signal to astrain signal.

Example #5: The pump monitoring system of example(s) 1-4 wherein thevibration detector comprises an accelerometer.

Example #6: The pump monitoring system of example(s) 1-5 wherein thevibration detector comprises an acoustic or vibration transducer.

Example #7: The pump monitoring system of example(s) 1-6 wherein thevibration detector comprises a torque transducer positionable at atorque input for a pump section that includes the sensor.

Example #8: A method of identifying a failed sensor includes receiving,by a processor, a sensor signal from a sensor in or on a fluid end of apump, and a vibration signal from a vibration detector, identifying, bythe processor, an irregularity in the sensor signal, determining, by theprocessor, whether an operational signal component is present in thevibration signal, and displaying, by the processor, an indication thatthe sensor has failed when the operational signal component is absentfrom the vibration signal.

Example #9: The method of example 8 further comprising detecting asquare wave like component in the vibration signal.

Example #10: The method of example(s) 8 or 9 further comprising applyingan order tracking filter to the vibration signal to detect the squarewave like component.

Example #11: The method of example(s) 8-10 further comprising comparingthe vibration signal to a strain signal.

Example #12: The method of example(s) 8-11 wherein the vibrationdetector comprises an accelerometer.

Example #13: The method of example(s) 8-12 wherein the vibrationdetector comprises an acoustic or vibration transducer.

Example #14: The method of example(s) 8-13 wherein the vibrationdetector comprises a torque transducer positionable at a torque inputfor a pump section that includes the sensor.

Example #15: A non-transitory computer-readable medium that includesinstructions that are executable by a processor for causing theprocessor to identify a failed sensor in a pump associated with awellbore, by performing operations including receiving a sensor signalfrom a sensor in or on a fluid end of a pump, and a vibration signalfrom a vibration detector, identifying an irregularity in the sensorsignal, determining whether an operational signal component is presentin the vibration signal, and displaying an indication that the sensorhas failed when the operational signal component is absent from thevibration signal.

Example #16: The computer-readable medium of example 15, wherein theoperational signal component comprises a square wave like component inthe vibration signal.

Example #17: The computer-readable medium of example(s) 15 or 16,wherein the operations further comprise applying an order trackingfilter to the vibration signal.

Example #18: The computer-readable medium of example(s) 15-17, whereinthe operations further comprise comparing the vibration signal to astrain signal.

Example #19: The computer-readable medium of example(s) 15-18 whereinthe vibration detector comprises an accelerometer or an acoustic orvibration transducer.

Example #20: The computer-readable medium of example(s) 15-19 whereinthe vibration detector comprises a torque transducer positionable at atorque input for a pump section that includes the sensor.

Example #21: A pump monitoring system for use in wellbore operationsincluding a sensor on a fluid end of a pump to provide a sensor signal,a vibration detector positionable to measure vibration and provide avibration signal, and a computing device couplable to the sensor and thevibration detector. The computing device includes a processor for whichinstructions executable by the processor are used to cause the processorto receive the sensor signal and the vibration signal, identify anirregularity in the sensor signal, determine, by processing thevibration signal, whether an operational signal component is present inthe vibration signal, and display an indication that the sensor hasfailed when the operational signal component is absent from thevibration signal.

Example #22: The pump monitoring system of example 21, wherein theinstructions are executable to detect a square wave like component inthe vibration signal.

Example #23: The pump monitoring system of example(s) 21 or 22, whereinthe instructions are executable to apply an order tracking filter to thevibration signal to detect the square wave like component.

Example #24: The pump monitoring system of example(s) 21-23, wherein theinstructions are executable to correlate the vibration signal to astrain signal.

Example #25: The pump monitoring system of example(s) 21-24 wherein thevibration detector comprises an accelerometer.

Example #26: The pump monitoring system of example(s) 21-25 wherein thevibration detector comprises an acoustic or vibration transducer.

Example #27: The pump monitoring system of example(s) 21-26 wherein thevibration detector comprises a torque transducer positionable at atorque input for a pump section that includes the sensor.

Example #28: A method of identifying a failed sensor includes receiving,by a processor, a sensor signal from a sensor in or on a pump,receiving, by the processor, a vibration signal from a vibrationdetector, identifying, by the processor, an irregularity in the sensorsignal, determining, by the processor, whether an operational signalcomponent is present in the vibration signal, and displaying, by theprocessor, an indication that the sensor has failed when the operationalsignal component is absent from the vibration signal.

Example #29: The method of example 28 further comprising detecting asquare wave like component in the vibration signal.

Example #30: The method of example(s) 28 or 29 further comprisingapplying an order tracking filter to the vibration signal to detect thesquare wave like component.

Example #31: The method of example(s) 28-30 further comprising comparingthe vibration signal to a strain signal.

Example #32: The method of example(s) 28-31 wherein the vibrationdetector comprises an accelerometer.

Example #33: The method of example(s) 28-32 wherein the vibrationdetector comprises an acoustic or vibration transducer.

Example #34: The method of example(s) 28-33 wherein the vibrationdetector comprises a torque transducer positionable at a torque inputfor a pump section that includes the sensor.

Example #35: A non-transitory computer-readable medium that includesinstructions that are executable by a processor for causing theprocessor to perform the method of example(s) 28-34.

The foregoing description of the examples, including illustratedexamples, has been presented only for the purpose of illustration anddescription and is not intended to be exhaustive or to limit the subjectmatter to the precise forms disclosed. Numerous modifications,combinations, adaptations, uses, and installations thereof can beapparent to those skilled in the art without departing from the scope ofthis disclosure. The illustrative examples described above are given tointroduce the reader to the general subject matter discussed here andare not intended to limit the scope of the disclosed concepts.

What is claimed is:
 1. A pump monitoring system for use in wellboreoperations, comprising: a strain sensor on a fluid end of a pump tomeasure properties associated with the pump and provide a strain signal;a vibration detector positionable to measure vibration associated withthe pump and provide a vibration signal; and a computing devicecouplable to the strain sensor and the vibration detector, the computingdevice including a processor for which instructions executable by theprocessor are used to cause the processor to: receive the strain signaland the vibration signal; identify an irregularity in the strain signalcorresponding to a potential strain sensor failure; determine, byprocessing the vibration signal, that an operational signal componentcorresponding to an irregularity in the pump function is not present inthe vibration signal, corresponding to a failure of the strain sensorthat indicates that the strain sensor is disconnected from the pump; anddisplay an indication that the strain sensor has failed in response todetermining that the operational signal component is absent from thevibration signal.
 2. The pump monitoring system of claim 1, wherein theinstructions are executable to detect a square wave like component inthe vibration signal.
 3. The pump monitoring system of claim 2, whereinthe instructions are executable to apply an order tracking filter to thevibration signal to detect the square wave like component.
 4. The pumpmonitoring system of claim 2, wherein the instructions are executable tocorrelate the vibration signal to a strain signal.
 5. The pumpmonitoring system of claim 1 wherein the vibration detector comprises anaccelerometer.
 6. The pump monitoring system of claim 1 wherein thevibration detector comprises an acoustic or vibration transducer.
 7. Thepump monitoring system of claim 1 wherein the vibration detectorcomprises a torque transducer positionable at a torque input for a pumpsection that includes the strain sensor.
 8. A method of identifying afailed strain sensor in a wellbore, the method comprising: receiving, bya processor, a strain signal from a strain sensor in or on a fluid endof a pump, and a vibration signal from a vibration detector;identifying, by the processor, an irregularity in the strain signalcorresponding to a potential strain sensor failure; determining, by theprocessor, that an operational signal component corresponding to anirregularity in the pump function is not present in the vibrationsignal, corresponding to a failure of the strain sensor that indicatesthat the strain sensor is disconnected from the pump; and displaying, bythe processor, an indication that the strain sensor has failed inresponse to determining that the operational signal component is absentfrom the vibration signal.
 9. The method of claim 8 further comprisingdetecting a square wave like component in the vibration signal.
 10. Themethod of claim 9 further comprising applying an order tracking filterto the vibration signal to detect the square wave like component. 11.The method of claim 9 further comprising comparing the vibration signalto a strain signal.
 12. The method of claim 8 wherein the vibrationdetector comprises an accelerometer.
 13. The method of claim 8 whereinthe vibration detector comprises an acoustic or vibration transducer.14. The method of claim 8 wherein the vibration detector comprises atorque transducer positionable at a torque input for a pump section thatincludes the strain sensor.
 15. A non-transitory computer-readablemedium that includes instructions that are executable by a processor forcausing the processor to identify a failed strain sensor in a pumpassociated with a wellbore, by performing operations comprising:receiving a strain signal from a strain sensor in or on a fluid end of apump, and a vibration signal from a vibration detector; identifying anirregularity in the strain signal corresponding to a potential strainsensor failure; determining that an operational signal componentcorresponding to an irregularity in the pump function is not present inthe vibration signal, corresponding to a failure of the strain sensorthat indicates that the strain sensor is disconnected from the pump; anddisplaying an indication that the strain sensor has failed in responseto determining that the operational signal component is absent from thevibration signal.
 16. The non-transitory computer-readable medium ofclaim 15, wherein the operational signal component comprises a squarewave like component in the vibration signal.
 17. The non-transitorycomputer-readable medium of claim 16, wherein the operations furthercomprise applying an order tracking filter to the vibration signal. 18.The non-transitory computer-readable medium of claim 16, wherein theoperations further comprise comparing the vibration signal to a strainsignal.
 19. The non-transitory computer-readable medium of claim 15wherein the vibration detector comprises an accelerometer or an acousticor vibration transducer.
 20. The non-transitory computer-readable mediumof claim 15 wherein the vibration detector comprises a torque transducerpositionable at a torque input for a pump section that includes thestrain sensor.